From my personal experience, it depends on the number of players you expect and their computers.
3000Kb seems a pretty reasonable limit for people with pretty decent computers and 15~20 people around.
It also depend on the number of visual effect object that tend to have some impact on the overall performances so it's better to limit smoke, fire etc.
Also keep in mind that the computer render what is displayed on the screen. If you have several "closed" rooms around your place they will be more performance friendly than if you have huge windows all around and that you can see almost all of your map from where you stand.
Good luck and have fun